Comment 1 for bug 1040085

Dear all,

The difference in rise/set times with respect to those of USNO has an explanation. As far as I know, they take into account refraction effects. Currently, the Observability plugin doesn't consider refraction. The same argument can be used for the Moon.

Regarding the changes in the rise/set time predictions as time goes by, this bug is also definitely related to the refraction effect. If you turn refraction off by removing the atmosphere, the predictions do not depend on time anymore. I thought that the "equinoxEquToAltAz" core function was returning the Alt/Az coordiantes free of refraction effects (which doesn't seem to be the case?). That of course affects the time predictions as a function of the Alt/Az coordinates, since the plugin was assuming that those coordinates were free of refraction effects. This bug can be easily solved by asking the core to give the geometric (i.e., not apparent) Az/Alt coordinates to the Observability plugin. I'll take a look to it asap.

On the other hand, I'm afraid that it will be more complicated to fully implement refraction, since some numerical approach should be used for all the objects (i.e., not only Solar-system objects, but also stars), e.g., by solving for the time of the (refraction-considered) null altitude. I would need to learn a bit about the refraction-related functions in Stellarium to solve this issue.